Articles

You probably haven’t noticed, but the length of a day is not what it used to be. Though only on the order of a few milliseconds’ difference and observable only over a period of decades, the time it takes the Earth to make one revolution varies.

I hate to pick nits, but it's the time for one rotation, not one revolution, that varies. Rotation, of course, is angular motion about a body's own axis, while revolution is angular motion around an external body (in this case, the sun).

As scientists, we need to be precise in our terminology, to avoid misleading the general public. In this case, even the "IEEE Spectrum Tech Alert" <techalert@ieee.org> editor was misled, sending a "clarified" summary whose first sentence reads, "The time it takes Earth to make one revolution around the sun varies."

Please get your rotation/revolution terminology correct. The earth rotates about its axis and revolves around the sun. The time of one rotation is a day; the time of one revolution is a year.

Unfortunately, this Science paper is not the best example of fair scientific practices. The ideas advertised there were described in detail in our previous publications:

1. Oganov A.R., Ono S. (2005).
The high pressure phase of alumina and implications for Earth’s D” layer.
Proc. Natl. Acad. Sci. 102, 10828-10831.

2. Ono S., Oganov A.R., Koyama T., Shimizu H. (2006). Stability and compressibility of high-pressure phase of Al2O3 up to 200 GPa: implications for electrical conductivity at the base of the lower mantle.
Earth Planet. Sci. Lett. 246, 326-335.

The first paper was not cited, and the second one was referred to very parenthetically. The ideas about the electrical conductivity of post-perovskite being ~2 orders of magnitude higher than that of perovskite, and the implications for the electromagnetic coupling between the mantle and core were described in detail in those papers. The main (and indeed significant) achievement of the Science paper of Ohta and Hirose is the direct measurement of the conductivity, but they failed to properly acknowledge the previous prediction and detailed discussions of the issue.

This kind of competition is not new. When we (my colleague S. Ono and I) and Hirose's group simultaneously reported the discovery of post-perovskite, there was a similar story. In the present case it is not possible to claim simultaneity, as our work was published years before.